I doubt either line will top SP either (which honestly I do not think is that expensive anyway) but the reason is because neither line really has the kids now. if JLU had a large children following though I would expect it would surpass SP but I don't think it really did plus alot more people actually keep figures mint and MOC these days so that is working against it too. SP is more rare as you said and also hard to find in good condition because most people played with their toys then.

The only pricey bits I've seen from Super Powers is Cyborg... the foreign items... and the un-produced items like the Darkseid's playset. Everything else seems rather affordable here and there depending on how much you want to shop around and if you're not collecting mint on card.

it lives.